WASHINGTON, April 25 (Reuters) - U.S. Senate leaders arefrantically trying to put together a plan to alleviatewidespread airline flight delays caused by last month'sautomatic federal spending cuts, working on legislation thatcould be voted on as early as Thursday.

Under bipartisan legislation that is all but ready to bepresented to the full Senate, the Department of Transportationwould be given new flexibility to take unspent funds and usethem to cover the costs of air traffic controllers and otheressential employees at the Federal Aviation Administration.

"It's a matter of dotting i's and crossing t's," said oneSenate aide familiar with the discussions.

Once a deal is reached among senators and the White House,Senate leaders would seek quick passage. If passed, the House ofRepresentatives then could hold a quick vote, ending anotherchapter in a series of Washington battles over budget and taxesthat have been waged since 2011.

Lawmakers are eager to find a fix before they head out oftown for next week's congressional recess. They are concernedabout deepening public resentment over the delays caused by thefurloughs of controllers.

Airline passengers have grown increasingly irritated overthe past week with delays at major hubs like Chicago, New York,Los Angeles and Atlanta. Some have reported delays of severalhours in takeoff times and planes being put in holding patternsin the air. Many pilots blame furloughs for landing delays.

The National Air Traffic Controllers Association on Thursdaysaid that many of the 1,978 controller trainees are now workingfull shifts by themselves to help cover staffing shortages.

And airline executives ratcheted up their complaints. "Thisis government not working - capital letters, exclamation point -when we're sitting here holding the traveling public hostage inthe midst of sequestration," JetBlue Chief ExecutiveDave Barger said on a conference call on Thursday.

The FAA has said it had no alternative to furloughingcontrollers this week after Congress failed to come up with abudget deal that would have averted the $85 billion inacross-the-board federal spending cuts between March 1 and Sept.30.

At the same time, the FAA has emphasized that passengersafety is not at risk. Airlines for America, the tradeorganization for U.S. airlines, also said on Thursday that thefurloughs have not created a safety issue.

"These are simply irresponsible cuts that have real anddetrimental impacts on the traveling public, on the airlineindustry, on the hospitality industry," Republican Senator SusanCollins of Maine said on the Senate floor. Collins is one of thenegotiators on the bill being written.

While Republicans are joining the effort for a quick fix,many have been skeptical about whether the White House and FAAare taking advantage of flexibility they already have.

Republicans have accused the Obama administration ofmaximizing the disruptions to try to shift budget blame onRepublicans - an allegation the administration has denied. Republicans have created a Twitter hashtag, #Obamaflightdelays,for people to complain about the delays.

However, a congressional aide involved in the originalautomatic spending cut legislation that was enacted in August2011 told Reuters that the administration cannot under currentlaw shift money from outside accounts to fund the air trafficcontroller account.

SEQUESTRATION FALLOUT

The FAA has said it will have to furlough 47,000 employeesfor up to 11 days through Sept. 30 in order to save $637 millionthat is required by the "sequestration," automatic spending cutsthat started on March 1 for most federal agencies.

Of those 47,000 workers, almost 15,000 are full-time airtraffic controllers or trainees.

The FAA issued an update that said more than 863 delays inthe system on Wednesday were attributable to staffing reductionsresulting from the furloughs.

An additional 2,132 delays were attributed to weather andother factors, the FAA said. The agency said it would work withairlines to minimize delays.

Airlines, many of which are reporting earnings this week,have pushed the government to quickly ease the flight delayscaused by the furloughs.

Jeff Smisek, chairman and chief executive of UnitedContinental Holdings Inc, said his company's networkoperations center is working around the clock to minimize theimpact of fewer controllers.